Photographic light balancing method



May 11, 1954 J. A. GlBBoNs 2,678,273

PHOTOGRAPHIC LIGHT BALANCING METHOD l Original Filed July 26, 1948 Naf IN VEN TOR. JMES G/BBONS Patented May 11, 1954 UNITED STATES ATENT OFFICE PHOTOGRAPHIC LIGHT BALANCING METHOD James A. Gibbons, North Hollywood, Calif., assignor to Warner Brothers Pictures, Inc., 'Burbank, Calif., a corporation of Delaware Original application July 26, 1948, Serial No. 40,666. Divided and this application May 14,

1949, Serial No. 93,339

3 Claims. (Cl. 95-5) the light filter screen.

In the art of motion picture production, many scenes within the camera viewing angle are illuminated by a combination of daylight and articial light, or parts of the scene are illuminated with daylight and other parts with artificial light. For instance, in the photographing of an indoor scene of a room, the camera angle may include a portion of the interior illuminated by normal artificial light and a window or door through which an outside area is seen by the camera, the outdoor area being illuminated by intense sunlight. Under these conditions, the outside area has a very strong illumination, and it is impractical to illuminate the interior to the same intensity for several reasons, such as the necessity for many lamps, the elimination of detail in the shadows, and inconvenience to the actors. However, by reducing the light intensity from the outside area, the indoor area may be artificially illuminated in the normal manner, and the lrn will be properly exposed, and thus, provide a better quality picture.

The present invention, therefore, is directed to a neutral density light reducing screen which reduces the light over all wavelengths of the visible spectrum in equal amounts, so that the exposure of the outside area and interior will have the same dennition and proper proportioning in the Viinished print. Such a screen is one in which dye is applied and absorbed by the screen, the dye absorbing the light, and thus, producing the reduction in light reaching the camera nlm. The screen is made of multiple coats of plastic materialyis light, tough, and,l when mounted in its frame, may be easily moved about to the desired locations.

The principal object of the invention, therefore, is to facilitate the obtaining of light intensity balances between areas having diierent illuminations.

Another object of the invention is to provide an improved method of balancing the light intensity between 4various area-s having different illuminations.

A further object of the invention is to provide 'an improved method of illuminating or lighting a scene to be photographed, and having different illumination in portions thereof, to provide optimum light intensities for the photographic emulsion.

.Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the appended claims, the manner of its organization and the mode of its operation will be better .understood by referring to the following description, read in conjunction with the accompanying drawings, forming a part hereof, in which:

Fig. 1 is a diagrammatic view showing one use of the invention.

Fig. 2 is an elevational View of the screen mounted in its frame, and

Fig. 3 is an enlarged cross-sectional View il- Alustrating the construction of the screen.

Referring now to the drawings, a camera' is set up within an interior 6, the camera yviewing angle being within the dot-and-dash lines 1. The scene within the angle may constitute the walls it and H of a room, counters or tables I2 and i3, andactors IEvand l1, theractor I6 walking from the positionl-s to the position i6 during the sequence. The room has a door 42) and a window 2 I, the camera, of course, photographing viewable objects through the door and window, such as a building 24 and sidewalks 25 and 2S, the sidewalks being on the sides of a street-21. In photographing such a scene, .it is obvious that the camera will not only see the interior, but also the exterior through door 2li and window 2 l, and that the exterior may be illuminated by intense daylight, while the interior is illuminated by artificial light. If suiiicient articial light were supplied to the interior to balance the intense daylight of the exterior, the interior light would be so intense as to be impractical for the reasons mentioned above. Thus, to permit the use of normal artificial light, the street light is reduced by the positioning of a screen 3D in front of the door and window, which screen is made in accordance With the invention.

Referring now to-Fig. 2, the screen 30 is mount ed inthe usual manner within a rigid frame 3| and laced by rubber bands or cords 32 through gromets in the screen and holes in the frame.

lReferring now to Fig. 3, the screen is shown for purposes of illustration as made up of a plurality of coats or layers 3ft, in which the two last layers on the right are shown impregnated by a dye. Although the dye is shown in only these layers, it is to be understood that it may extend to only one layer or into more than two layers in accordance with the amount of light reduction required. lzlurthernfiorefsince'each layer 0r coat is of the same material, there is actually no line of separation between layers, the screen being homogeneous.

Referring now to the actual construction of the screen, it is built up in layers or coats, each coat being applied as a solution to a pre-prepared matrix made in accordance with my co-pending appllcation, Ser. No. 40,667, filed July 26, 1948, now Patent No. 2,558,244. The screen is made of a formula `which I refer to as M-3, and given hereinafter, the dye being applied after the required number of coats have been applied to build the screen up to the desired thickness. For instance, the base solution iiist placed in a dip-pan and the surface of a matrix on a cylindrical drum is passed therethrough to apply each coat, which is dried before the application of the next coat. The base is generally of sufficient tensile strength and toughness after the application of six coats, which provides a screen of substantially .007 inch thick. The formula for the base layers is as follows:

Ethyl cellulose -gms 744 Xylol cc 3468 Ethylene glycol monomethyl ether cc 827 Butyl alcohol cc 827 Methyl isobutyl ketone cc 827 Methyl 4phthalyl ethyl glycollate cc 43 The above formula is adjusted to a viscosity ol 42 at 24 degrees C., the application speed for a drum of approximately live feet, ten inches in diameter, being one revolution in sixteen minutes. The formula for the dye coat solvents is as follows:

The solvents and dyes are thoroughly mixed and placed in a dip-pan and applied by revolving the drum, and thus, rotating the homogeneous base. The base is allowed to dry for at least two hours before applying the dye coat.

The above screen has a neutral density, and by Varying the dye coat, will produce diflerent amounts of light reduction, the above formula being that used for bright sunlight to balance normal artificial light in an interior such as illustrated in Fig. 1. That is, the above dye formula provides sixty-inve percent absorption of light7 only one dye coat being applied at a drum speed of one revolution in ten minutes, the drum having a diameter of approximately five feet, ten inches. To vary the absorption, the drum speed is varied. For instance, to determine the drum speed for a specic value of light absorption; a drum having an approximate circumference of iifteen feet has its speed varied each three feet, thus providing live test strips. This permits a graph of drum speed versus light transmission to be made, the drum being rotated at a constant selected speed for the final screen, the dye being uniformly applied to the entire screen.

1f the desired absorption is not Within the range of speeds selected for proper application of the dye coat, the dye formula may be strengthened or weakened by proportionately increasing the dye ingredients with respect to the solvents and another series of speed tests made. By comparing the strips with established iilters of known absorptions, using the log sector for photo-spectrometer tests, the desired speed of rotation for the drum is determined.

The screen is cut by strings placed under the last coat of the base and then stripped from its matrix and placed in the frame 3l of proper size. It is then ready for use as described above.

I claim:

l. The method of photographing an area at least one portion of which has a normal high intensity of illumination, and another portion of which has a normal low intensity of illumination, comprising illuminating said portion of normal low intensity illumination to an intensity required by the photographic emulsion of. any type being used for photographing, and reducing the illumination of said portion having the normal high intensity illumination by a separate removable iilter screen between said last mentioned portion and said emulsion, said lter screen reducing light over all wave lengths of the visible spectrum in substantially equal amounts.

2. The method of equalizing the light intensities between two areas to be photographed,`

simultaneously on a certain photographic emulsion of any type, one area having a high light intensity and the other area having a low light intensity, said low light intensity area to be photographed separately with a low light intensity, comprising adjusting the illumination in said low light intensity area to the light intensity value necessary for the proper exposure of said emulsion and nltering with a separate nlter screen placed in said high light intensity area adjacent said low light intensity area, all light frequencies to the same degree coming from said high light intensity area to said emulsion te correspond to the adjusted illumination in said low light intensity area, said filter being removed when said area of said low light intensity is photographed separately.

3. The method of equally exposing a photographic emulsion of any type to an action scene, one portion of which is outdoor and illuminate with one light intensity, and another portion of which is indoors and illiuninated with a lower light intensity, comprising determining the intensity of illumination of said indoor portion of said scene dependent upon the type of said photographic emulsion, illuminating said portion at said intensity, and inserting a separate filter screen in said outdoor portion adjacent said indoor portion to reduce the light intensity of said outdoor portion as impressed on said emulsion in accordance with the difference between the illuminations of said portions, said filter screen reducing light over all wave lengths of the visible spectrum in substantially equal amounts.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,742,630 Artigue Jan. 7, 1930 1,764,490 Artigue June 17, 1930 

1. THE METHOD OF PHOTOGRAPHING AN AREA AT LEAST ONE PORTION OF WHICH HAS A NORMAL HIGH INTENSITY OF ILLUMINATION, AND ANOTHER PORTION OF WHICH HAS A NORMAL LOW INTENSITY OF ILLUMINATION COMPRISING ILLUMINATING SAID PORTION OF NORMAL LOW INTENSITY ILLUMINATION TO AN INTENSITY REQUIRED BY THE PHOTOGRAPHIC EMULSION OF ANY TYPE BEING USED FOR PHOTOGRAPHING, AND REDUCING THE 